Fail-safe alarm system utilizing frequency modulated signal detection
First Claim
1. An alarm system for monitoring selected conditions at a remote location and providing a signal representative of the presence or absence of an alarm condition at the monitored location or power failure at either monitored or monitoring location, comprising:
- (a) a transmitter at said monitored location, said transmitter comprising;
(i) frequency generator means for continuously generating a first output signal at a predetermined nominal frequency;
(ii) means for modulating the frequency of said first output signal;
(iii) means responsive to an alarm condition at said monitored location for disabling said frequency modulating means;
(b) a receiver at said monitoring location connected to said transmitter, said receiver comprising;
(i) first circuit means for detecting the absence of modulation of said first output signal and generating a second output signal representative thereof;
(c) second circuit means responsive to said second output signal of said first circuit means and to loss of power for generating a time-delayed signal representative of said alarm condition or loss of power.
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Accused Products
Abstract
An alarm system for transmitting an alarm signal between remote locations utilizing frequency shift keying over conventional power lines. The alarm system includes a transmitter having a nominal frequency and circuitry for modulating the transmitter frequency. Upon detection of an alarm condition the modulating circuitry is disabled. A receiver is provided and has circuitry for detecting the presence or absence of modulation of the transmitter frequency. The receiver generates an alarm signal upon detection of absence of modulation and power failure of the system. The alarm signal is time-delayed to prevent nuisance alarms.
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Citations
9 Claims
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1. An alarm system for monitoring selected conditions at a remote location and providing a signal representative of the presence or absence of an alarm condition at the monitored location or power failure at either monitored or monitoring location, comprising:
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(a) a transmitter at said monitored location, said transmitter comprising; (i) frequency generator means for continuously generating a first output signal at a predetermined nominal frequency; (ii) means for modulating the frequency of said first output signal; (iii) means responsive to an alarm condition at said monitored location for disabling said frequency modulating means; (b) a receiver at said monitoring location connected to said transmitter, said receiver comprising; (i) first circuit means for detecting the absence of modulation of said first output signal and generating a second output signal representative thereof; (c) second circuit means responsive to said second output signal of said first circuit means and to loss of power for generating a time-delayed signal representative of said alarm condition or loss of power.
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2. An alarm system for monitoring selected conditions at a remote location and providing a signal representative of the presence or absence of an alarm condition at the monitored location or power failure at either the monitored or monitoring location, comprising:
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(a) a transmitter at said monitored location, said transmitter comprising; (i) frequency generator means for generating a first output signal at a predetermined nominal frequency; (ii) means for modulating the frequency of said first output signal; (iii) means responsive to an alarm condition at said monitored location for disabling said frequency modulating means; (b) a receiver at said monitoring location, connected to said transmitter, said receiver comprising; (i) first circuit means for detecting the presence or absence of modulation of said first output signal and generating a second output signal representative thereof; (c) second circuit means responsive to said second output signal of said first circuit means and to loss of power for generating a time-delayed signal representative of said alarm condition or loss of power, said second circuit means comprising; (i) switch means having a first state corresponding to non-alarm and power ON conditions and a second state corresponding to an alarm condition or power failure of said alarm system; (ii) time delay circuit means for switching said switch means between said first and said second states, said time delay circuit means having means for biasing said switch means in said first state in response to the presence of modulation of said first output signal and system power, said time delay circuit means operable a predetermined time following receipt of a signal indicating absence of modulation of said first output signal or power failure to switch said switch means to said second state whereby said switch means generates an alarm signal. - View Dependent Claims (3, 4, 5)
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6. An alarm system for monitoring selected conditions at a remote location and providing a signal representative of the presence or absence of an alarm condition at the monitored location or power failure at either monitored or monitoring location, comprising:
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(a) a transmitter at said monitored location, said transmitter comprising; (i) a ceramic resonator having an output signal with a nominal predetermined frequency; (ii) a timer circuit connected to said resonator for generating a frequency modulation signal; (iii) a capacitor selectively connected in parallel with said resonator; (iv) switch means connecting in series with said capacitor and responsive to said modulating signal for selectively connecting and disconnecting said capacitor in parallel with said ceramic resonator whereby said output frequency of said resonator is modulated about said nominal frequency at a rate corresponding to the frequency of said signal generated by said timer circuit (v) means responsive to an alarm condition at said monitored location for disabling said frequency modulating means; (b) a receiver at said monitoring location connected to said transmitter, said receiver comprising; (i) first circuit means for detecting the presence or absence of modulation of said output signal of said ceramic resonator and generating a second output signal representative thereof; (ii) second circuit means responsive to said second output signal of said first circuit means and to loss of power for generating a time-delayed signal representative of said alarm condition or loss of power. - View Dependent Claims (7)
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8. An alarm system for transmitting an alarm signal between remotely located points, comprising:
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(a) a transmitter, said transmitter having means for generating a first signal in response to detection of an alarm condition; (b) a receiver connected to said transmitter and having means for detecting the presence or absence of said first signal and generating a second signal representative of the presence of said first signal; and (c) an alarm trigger circuit having a circuit means responsive to said second signal and to loss of power for generating a time-delayed alarm signal, said alarm trigger circuit comprising; (i) switch means having a first state corresponding to non-alarm and power ON conditions and a second state corresponding to an alarm condition or power failure of said alarm system; and (ii) time delay circuit means for switching said switching means between said first and said second states, said time delay circuit means having means for biasing said switch means in said first state and switching said switch means to said second state following a predetermined time following receipt of said second signal or power failure. - View Dependent Claims (9)
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Specification